WASHINGTON -- After a three-month winning streak, the House Republican "Contract with America" is likely to suffer a stinging defeat tomorrow with the expected failure of a constitutional amendment limiting congressional terms.

Advocates of term limits -- highly popular with voters -- are still hoping that last-minute pressure will help them avoid what would be the first loss in the House for any of the 10 major elements of the contract -- and a particularly embarrassing one.

"This is the only vote on an issue of self-interest in the contract," said Rep. Bob Inglis, a South Carolina Republican. "We're arguing that it's the political equivalent of a vote on a congressional pay raise and that members should think twice before they vote against it."

Yet, with many senior members of both parties opposed to term limits, supporters say they are still about 60 votes short of the 290 needed to pass a constitutional amendment.

Four alternate versions of the amendment are scheduled to be voted upon tomorrow, with proposals to limit two-year House terms ranging from a minimum of three to a maximum of six. Each of the plans would set two six-year terms for the Senate.

But none of the alternatives is expected to have close to the required two-thirds majority.

At least one advocacy group is openly questioning the commitment of the House GOP leadership, which has agreed to bring all four options to the floor for a vote, thus permitting every congressman to support a term limit proposal without any single one's passing.

"I see it as a public relations campaign designed to look good while what they're doing is phony," Paul Jacob, executive director of U.S. Term Limits, a grass-roots advocacy group, said of tomorrow's vote.

Republican leaders, meanwhile, are positioning themselves to blame the Democrats, without whose help the 230-member GOP majority can't reach the 290 votes needed.

"We have more disagreement over term limits [than other items in the contract], but everybody knew that last year," House Speaker Newt Gingrich said yesterday of the Republicans.

But he predicted that four-fifths of GOP House members would support the amendment, and asserted that it would pass if half the 204 Democrats joined them.

Mr. Gingrich said party leaders "are not going to try to muscle" GOP members who oppose term limits. "On constitutional amendments, people have to be allowed to vote their conscience," the speaker added at a meeting with reporters in his suburban Atlanta district.

They contend that without experienced members, Congress would be run by unelected staff aides and lobbyists.

Most of the support for term limits is coming from junior House members, many of whom were elected on campaign promises to support the proposal.

But there is vigorous philosophical opposition even among some freshman, such as Rep. Robert L. Ehrlich Jr., a Baltimore County Republican.

"The Constitution already provides a way to get rid of House members every two years, and we've seen that works very well," Mr. Ehrlich said. "It's actually become a disadvantage to be an incumbent."

Congressional turnover has been so high in recent years that more than half of the members of the House have been elected since 1990.

As a result of last year's elections, Republicans gained control of both houses of Congress for the first time in two generations. Despite Mr. Gingrich's contention that arms are not being twisted, Mr. Inglis said, "There is tremendous pressure on Republicans to vote 'yes' for term limits."

He said GOP polls show that term limits is one of two issues in the GOP contract with which voters identify most strongly. The other is the constitutional amendment to balance the budget, which passed the House in January but was defeated by one vote in the Senate.

"We didn't promise to pass these things just to vote on them," Mr. Inglis said. "But I think the perception may be different."

The GOP contract, a campaign document issued last fall that listed major legislation the Republicans promised to bring to a vote during the first 100 days of this Congress, was designed to address issues most popular with the public.

A Time magazine/CNN poll taken last week revealed that support for congressional term limits remains just where it was shortly before the election, with 66 percent of those surveyed saying they support such limits, most favoring the shorter three-term -- or six-year -- option.

However, tomorrow's House vote may be more important to the Republicans, who have only two items to go before they complete their contract list next week, than it is to the term limits movement.

Twenty-two states already have imposed their own congressional limits, and at least one more is expected to do so this year.

If a U.S. Supreme Court ruling expected in June upholds those state laws, at least 95 congressional seats could be subjected to term limits by 1998. Another 60 or so would come under term limits by the year 2000.

Many of the rest of the states may have set their own limits by then.

"On the time line of the term limits movement, the real milestone of this year will be the Supreme Court decision," said Scott Rasmussen, chairman of the U.S. Term Limits Leadership Council, another advocacy group. "The House vote is largely irrelevant."

Even if a term limits proposal were to pass the House this week, the proposed amendment would face even grimmer prospects in the Senate.

"I think this is going to be one of those issues where Congress doesn't get involved until it's clear something is going to actually happen," Mr. Rasmussen said.